The invention is based on a method for operating an internal combustion engine installed in a motor vehicle having controlled intake and exhaust valves.
In the case of a known method for operating a valve-controlled internal combustion engine (DE 196 32 074 A1), on the crankshaft of which an electrical machine serving as “starter-generator” is coupled without a clutch, the valves are displaced—before the internal combustion engine is started or accelerated—by a valve-control unit so that practically no compression is produced in the internal combustion engine. The starter-generator, in motor operation with relatively low power, can then rev the crankshaft of the internal combustion engine with little power while drawing current from the battery via a frequency converter, whereby the starter-generator only has to overcome the moment of inertia of the internal combustion engine and its friction. Rewing takes place while ignition, fuel injection, and mixture formation are switched off. The valves are displaced in a manner known per se by controlling valve lift directly in appropriate fashion, or by changing the timing angle between camshaft and crankshaft accordingly. When a minimum speed of the internal combustion engine detected by a speed sensor and sent to a main electronic control unit is reached, the valves are adjusted via the valve-control unit and the valve-actuator drive so that, after ignition of the internal combustion engine is switched on, the combustion process for operating purposes is started, whereby the inertial energy applied previously by the starter-generator operating in the motor mode helps to start and accelerate the internal combustion engine in short time. As soon as ignition has taken place in the internal combustion engine, the motor operating mode of the starter-generator switches off and changes over to generator mode, which allows the starter-generator to recharge the battery.
A method of this nature is used to shut down the internal combustion engine in operating phases of the internal combustion engine when no power output is required, or to allow some of the cylinders to simply run along without ignition and compression, and, when power is required once more, to initiate a restart of the internal combustion engine by delivering kinetic energy. This results in reduced fuel consumption and emission of pollutants.
In the case of a known drive system (EP 0 847 488 B1) that comprises an internal combustion engine and an electrical machine coupled to its crankshaft and serving to actively dampen rotational non-uniformities of the crankshaft of the internal combustion engine, both the internal combustion engine and the electrical machine are controlled by a microcomputer control unit. In the framework of controlling the internal combustion engine, the microcomputer control unit performs the following control tasks: fuel supply control, throttle valve actuation, fuel injection control, ignition control, valve actuation, charging-pressure regulation, exhaust gas recirculation control, and start/stop control. The rotational non-uniformities are dampened in this manner: the electrical machine generates a rapidly alternating torque, namely, a braking torque for a positive rotational non-uniformity and a driving torque for a negative rotational non-uniformity, onto which it superimposes a positive or negative torque, respectively, in order to additionally accomplish a driving action or a braking, regenerative action.
In the case of a drive system of this type that is also known (DE 32 27 810 C2) and that is used as a hybrid drive, an additional clutch is situated between the crankshaft of the internal combustion engine and the electrical machine that is operated as a generator, starter-generator and/or driving motor, in order to interrupt the engine braking action on the vehicle on overrun and thereby recuperate as much of the vehicle's kinetic energy as possible and return it to energy accumulator, e.g., the vehicle battery, to extend the coasting phase of the vehicle, or to operate exclusively on electric power under low-load operation.